1. Field of the Invention
The present invention relates to electronic circuits for generating audio-frequency signals suitable for amplification and play through a loudspeaker, and whose characteristics can be tailored to provide a reasonable simulation of car or truck engine sounds, as we 1 as other sounds, for use primarily in toys and games.
2. Prior Art
A variety of methods have been used to generate vehicle engine sounds for use in toys, games and other such devices. The earliest of these were mechanical or electromechanical devices which spun toothed wheels against "flappers", either by means of an electric motor or by the "human power" of a child pushing the toy. However, these systems suffered from a lack of realism, large size, and mechanical complexity.
More recently, electronic devices have been incorporated into products to produce engine sounds. In some cases, actual sampled, digitized recordings of engine sounds have been used, played back either by a microcomputer, as in Nylint Corp.'s Sound Machine.TM., or by a specialized integrated circuit sound playback device, as in the case of the Sounds of Power.TM. product from Road Champs. These techniques provide good realism but at relatively high cost.
Other electronic simulations have been achieved by less expensive microcomputer algorithmic sound synthesis techniques which, however, provide less realism. Still lower cost, but with concomitantly less realism, have been achieved with simple circuits employing oscillators. The lack of realism results from the regularity and predictability at the output of the oscillator.